Looking Up: See Uranus next door to Jupiter

Basking in the glow of its big neighbor Jupiter, you can see another planet with binoculars the next clear night with the same view. Trailing closely with Jupiter right now is the planet Uranus.

Peter Becker

Basking in the glow of its big neighbor Jupiter, you can see another planet with binoculars the next clear night with the same view. Trailing closely with Jupiter right now is the planet Uranus.

These two worlds, along with Saturn and Neptune, make up the gas giants in our solar system’s family of planets. They are immense by earthly standards. Earth is not quite 8,000 miles wide. Compare that with the fifth planet Jupiter, booming at 87,000 miles across at the equator; sixth from the sun is Saturn, still a titan at 72,000 miles. Uranus and Neptune are about 31,000 and 33,000 miles wide.

We would expect Jupiter to dominate the night sky among the planets given its brilliance. In fact, only Venus is brighter, and only at certain times of the year. Jupiter is shining at magnitude -2.9, brighter than any star. Its bright white light is unmistakable as it rises in the eastern sky during the evenings this month.

Although the planet is on average 483.3 million miles from the sun, and about 380 million miles from Earth at its closest, this great light is still visible.

Uranus, however, is much dimmer. The seventh planet is presently magnitude 5.7; its average distance from the sun is 1,783 million.

The faintest star most people can see on a very dark and clear night in the countryside is six on the magnitude scale. While possible to see Uranus with the naked eye, it escaped detection until 1781 when astronomer Sir William Herschell stumbled upon it with his telescope. Nearly six on the magnitude scale, it easily blends in with a host of faint stars.

Binoculars, however, will show Uranus readily. This is an excellent time to look for it, too, with Jupiter as a guidepost. Between now and early December, the pair are close together, gradually shifting east to west against the background stars. Jupiter, being closer, gradually overtakes Uranus. But both will fit within one field of view of binoculars. They appear closest together on Sept. 18 when they are .8 degree apart. For comparison, the full moon spans about .5 degree.

With binoculars, Uranus appears as a dim but easily seen “star” just above brilliant Jupiter. No other stars of like brightness are close by to confuse identifying Uranus.
They both reach opposition –– when they are on the opposite side of the sky from the sun –– on Sept. 21. On that day they rise at approximately the same time as the sun sets, and they are visible all night long.

While a small telescope easily shows the disc of Jupiter with some details of its cloud bands and spots, the disc of Uranus appears much smaller. Resolving it with a telescope as a clean, circular disc isn’t easy because of air turbulence. It may appear slightly greenish, bluish or gray.

Neptune is visible in the southern sky in September this year with binoculars. Much farther out (averaging 2,793 million miles), the eighth planet appears as magnitude 7.8. Binoculars show it as a faint star among many dim stars. A good finder chart is needed to pick it out. The September 2010 issue of Sky & Telescope Magazine and the web site www.skyandtelescope.com both have charts for these outer planets.

The bright moon will stand above Jupiter and Uranus on Sept. 22; the full moon is on Sept. 23.